This invention relates to a sewing machine, and particularly to the type of industrial sewing machine that is capable of simulating hand stitching.
In such machines, movements of the needle and the workpiece are synchronized in such a way that the thread forms a first stitch lying above the workpiece, passes downwardly through the workpiece, forms a second stitch lying below the workpiece and then passes upwardly through the workpiece. The cycle is repeated to form a continuous line of stitching.
There are principally two types of machine that can operate in this way, the floating needle type and the latched needle type.
Floating needle machines utilize a needle having pointed upper and lower ends and an eye in a central region of the needle. An upper releasable needle holder is mounted for reciprocation above the throat plate of the machine and is capable of gripping the upper end of the needle. Similarly, a lower releasable needle holder is mounted for reciprocation below the throat plate and is capable of gripping the lower end of the needle. Means are provided for controlling the needle holder so that the needle is transferred from the grip of the upper needle holder to the grip of the lower needle holder as the needle moves downwardly from an upper position lying wholly above the throat plate to a lower position lying wholly below the throat plate. Similarly, the needle is transferred from the grip of the lower needle holder to that of the upper needle holder as the needle moves upwardly from the lower position to the upper position. Floating needle machines have a drum mounted below the work table of the machines, the drum having a periphery around which a length of thread may be wrapped by a looper mounted for rotation around the periphery of the drum.
Latched needle machines utilize a needle having a point on the lower end only, the thread being retained on the needle by a latch which is released after the needle has moved downwardly through the workpiece. The needle is then moved upwardly before further movement of the workpiece to release the thread below the workpiece. The workpiece is advanced, the needle moved downwardly and the thread is picked up and held on the needle by the latch. The needle moves upwardly to draw thread back above the workpiece, which is then advanced and the cycle repeated. Such machines again have a drum below the work table, the drum having a periphery around which a length of thread may be wrapped.
These known machines utilize pre-cut lengths of thread, provided to the machine operator in the form of a package. The package is usually suspended or otherwise held in a convenient location adjacent to the machine, and the operator takes single lengths of thread from the package as required, threads the needle of the machine and operates the looper so that the remainder of the length of thread is drawn into position around the periphery of the drum. As stitching proceeds, the looper rotates about the drum in synchronization with the needle, in order to draw free thread off the drum as required and then to place the free thread back into the drum.
Significant time and cost are involved in preparing the packets of pre-cut thread. Selection of individual thread lengths from the packet is not always easy, and requires the machine to be stopped while the operator performs this function. The invention seeks to overcome this problem.